1. Field of the Invention
The present invention relates to a method of reproducing encoded information.
2. Related Background Art
Hitherto, as a code utilized for recording information to a recording medium, there is a coding system in which a limitation (for example, the number of code "1"s is limited) is added to a weight of code, as shown in Zero Disparity code (ZD code) or Low Disparity code (LD code). The above codes are described in detail in e.g., "Tendency of Encoding System in High Density Recording" written by Saburo Tazaki and Hisashi Osawa, Vol 12, 1985. In such a coding system, the error may be reduced by utilizing the above limitation as information.
In a case where such a signal is magnetically or optically recorded on a recording medium with a RZ code and where a recorded digital signal is reproduced, generally, an attention is paid to the state of the analog waveform of the reproduction signal and a discrimination regarding 1 and 0 is executed.
For instance, an attention is paid to the level of the analog waveform of the reproduction signal, the reproduction signal is binarized by a comparator (a fixed binarization discrimination level), the binarized value is regarded as a code, and thereafter, the code is decoded.
However, as shown in FIG. 2, the actual reproduction signal waveform is accompanied with various fluctuations due to a local change of a recording medium, a tracking state, an interference between codes, and the like. Therefore, the code train of the reproduced signal does not always become the same code as the recorded code and a code error is caused.
On the other hand, FIG. 4 is a diagram showing conventional processes on the time base of the reproduction signal of NRZ code. In the case of FIG. 4, since the transition portion (zero cross point of the reproduction waveform) of the waveform of the signal obtained by binarizing the reproduction signal lies within a high level range of a time window signal, the result of the discrimination is "1".
However, as is well known, the transition portion has a time base fluctuation (what is called a jitter) due to the mechanical noises of the reproducing apparatus or the like and such a time base fluctuation results in a cause of the erroneous discrimination.
Such a problem occurs not only in the case where the signal is reproduced from a recording medium but also on the reception side when the signal was communicated.